To control the type of stitch and patterns in flatbed knitting machines and the like, a plurality of machine levers are positioned at predetermined individual levels by means of some lever positioning device. A common type of positioner is a chain carrying a series of links which in turn carry raised portions the height of each which determines the arrested position of the corresponding machine lever. The machine levers are spring-loaded in the forward direction and are alternately retracted and advanced against the chain by a machine operated bail. A given chain carries a number of combinations of raised portions and is stepped a predetermined number of steps each time a new combination is called for. The stepping takes place each time a new yarn carrier is presented to the machine levers calling for the new combination. The chain carrying its raised portions (program) is a passive arresting device since the machine levers are alternately retracted and then advanced against the program chain.
A given chain carries a given program consisting of a predetermined sequence of raised portions. In a complicated control pattern a chain may be very long and heavy. In order to change a program, the chain must be removed from the machine and a new program chain installed. This is a cumbersome and time consuming operation. In order to provide a new and previously unavailable program, a new chain must be designed and built, which is a costly operation.